Moderately high forming pressures and clamping forces are required to form thin foil sheet materials, particularly for low temperature forming, stamping and pressing operations. Such operations are hereafter referred to collectively as forming operations. Many of these forming operations use elastomeric or resilient surfaces in compression with the thin foil workpiece. Such surfaces include natural or synthetic rubber, polyurethane, filled cork, and other conventional elastomeric or resilient surfaces, hereafter generally referred to as resilient surfaces.
Wherever these pressures and forces bring a foil workpiece and resilient surfaces together, air is expelled from between the two, much like during compression of a suction cup. Because foils are compliant, air cannot easily re-enter the tight space between the foil and the resilient surface. After the forming operation is complete, the foil is left firmly adhered to the resilient surface and is often damaged during the process of its removal. This occurs whether large surface areas or annular or peripheral areas of the foil materials are compressed against the resilient surface.
Conventional forming operations such as hydroforming and rubber pad forming overcome these difficulties by sandwiching the thin foil between thicker sheets of steel. Heavier gauges of metal sheet materials such as steel can withstand the peel back force typically encountered with rubber diaphragms and pads. Since the steel plate(s), commonly referred to as cull plates, are formed along with the thin foil, they are not reusable and consequently exact a cost penalty in production.
Accordingly, improvements in forming thin foil sheet materials are needed to produce more cost effective shapes and products using thin foil materials.